FORAMINIFERS IN THE FOSSIL RECORD:
IMPLICATIONS FOR AN ECOLOGICAL ZONATION MODEL

Tammy ToskM.A. in Geology
San Bernardino, California

Do the sequence and diversity of foraminifers in the fossil record represent
evolutionary development, or are there alternative explanations?

The fossils in the geologic column have been thought to be a record,
although certainly not a complete record, of the development of life on Earth. Because the
prevailing paradigm assumes that the current processes operated at current rates in the
past, the fossil record is assumed to have been formed slowly as evolving plants and
animals lived, died and were buried, as we observe today.
Scientists working under that paradigm look for different kinds of
information than do those who assume that the fossil record is the result of a major
catastrophe. Because they think that fossils buried low in the geologic column must be
much older than and ancestral to those buried in the upper parts of the column, they look
for similarities and differences indicating evolutionary relationships.
Many scientists also assume that the fossils lived in the area where
they were buried and fossilized, only being transported before burial in ways similar to
those observed today. Fossils would thus give information about the environment of the
area where they lived and died.
If a major catastrophe such as the Noachian flood was involved, the
fossil distribution would be the result of factors other than just time and evolutionary
change. A scientist looking at the fossil record under a flood paradigm would assume that
most of the fossilized plants and animals had been living contemporaneously, and this
scientist would look for characteristics of the fossils that would explain their order of
burial during a major catastrophe. Some of the information needed for such an
interpretation is often included in the reports generally published, but much is not.
Species descriptions give information about the shape and structure of
the fossil, but may not give differences in size, thickness and weight that would be
significant in studies of their buoyancy and other transport characteristics. Differences
in preservation, which could be indicative of extensive transportation, are generally only
mentioned as problems for their identification. Stratigraphic occurrences (the vertical
range of the fossil in the geologic column) and geographic occurrences (the locations
where the species has been found) are generally given when known. However, only a small
fraction of the sedimentary rock in the crust of the earth has been examined for fossils,
so their true distribution and abundance can only be estimated.
Another problem with using published descriptions and stratigraphic
data is that fossils are often placed in different taxa, even in different superfamilies,
if they are found at different levels, even though they might be placed in the same genus
or species if found together. It is therefore difficult to recognize potentially
equivalent species in the geologic column.
Several questions must, however, be asked of the fossil record to
determine if its formation could have taken place within a short period of time. To show
the plausibility of a model in which a significant part of the geologic column was
deposited during a one-year, world-wide flood and its aftermath, one must show that all
the fossils in flood deposits could have been deposited or reworked during the flood
events into the observed biostratigraphy, and that similar organisms living after the
flood would have a biogeographic distribution and genetic variability consistent with the
loss of most of their population during the flood events.
To fully answer all these questions for all the fossil groups would
require many lifetimes of research. This paper will explore only the group with which I am
most familiar  the microfossils called foraminifers.

Significance of Foraminifers

Protozoans of the Order Foraminiferida have been used extensively
for relative dating of marine sedimentary rocks. They are small, generally less than a
millimeter in length, and often found in such abundance that hundreds of specimens can be
recovered from a mudstone sample with only a few hours of work. Because they are easily
recovered from drilling chips, they are used to correlate strata in oil wells. An
extensive literature of taxonomy and stratigraphic occurrences has therefore been
developed for economic as well as academic reasons.
Foraminifers have more architectural diversity than any other fossil
group. Many forms are long-ranging, being found through major segments of the fossil
record. Other more specialized forms have very restricted ranges, and so are useful as
index fossils. Foraminifers can therefore be used to correlate most marine sedimentary
deposits.

Foraminiferal Architecture and Mineralogy

Foraminifer shells, called tests, have many designs including simple
tubes, straight series of chambers, coils of chambers and even complex labyrinths. Their
walls can be formed of foreign particles agglutinated in organic or calcareous cement, or
totally of calcareous material secreted by the foraminifer. They interact with their
environment through pores in the test wall and apertures of varying shapes and sizes,
including some produced on long delicate necks. Foraminiferal taxonomy is based first on
the wall mineralogy and microstructure, then on chamber arrangement, apertural shape and
position, and ornamentation (Loeblich and Tappan 1964).

Foraminiferal Biology and Ecology

Foraminifers are abundant today and live in environments ranging
from deep sea trenches to estuaries and even freshwater lakes. Planktonic and pelagic
species live in the water masses at various depths, while benthic species live near, on or
in the sediment on the sea floor. Some are permanently attached to the substrate or to the
shell of another animal, but most are free living.
Pseudopodia, hair-like extensions of the foraminifer cell protoplasm,
are used for locomotion, for gathering food and building materials, and, with the aid of
adhesive material secreted by the foraminifer, for attaching to the substrate. In
planktonic species the pseudopodia are symmetrically distributed around the test, which is
also surrounded by frothy ectoplasm to aid in flotation. Because they have little control
of their movement, planktonic species are passive feeders, randomly attaching to organic
particles, algae, bacteria, or copepods which come into range of their pseudopodia
(Loeblich and Tappan 1964).
Some foraminifers attach to the sea floor and agglutinate sponge
spicules or other material into a tall branching structure to form a base for their
network of pseudopodia (Haynes 1981). They are also passive feeders.
Free-living species of both infaunal habit (living within the sediment)
and epifaunal habit (living on the sediment surface) are generally active feeders,
searching for food particles and prey. In burrowing species, the pseudopodia may form a
bundle at the aperture to move aside sediment grains. Foraminifers have been clocked at
velocities of several millimeters per hour while moving through coarse sand (Haynes 1981).
Foraminifers are tolerant of extreme conditions, with forms living in
areas of low oxygen levels, hyper- and hypo-salinity, and extremes of pH and temperature.
In deep ocean environments where calcareous material is dissolved, foraminifers with
agglutinated tests predominate (Haynes 1981). In nearly anoxic environments (<0.1 ml O2/l
water), foraminifers may be flattened to increase the surface area through which to absorb
oxygen (Douglas 1979). Their walls may be thinner and more porous, with less
ornamentation.
Within a single species the foraminifers may have thick ornamented
walls under normal oxygen concentrations, and thin, less-ornamented walls under low oxygen
conditions. In a study of Pliocene foraminifers (probably post-flood), Hendrix (1958)
broke open rocks containing both non-laminated massive and thinly laminated mudstone and
examined the foraminifers exposed on the fresh surfaces. He found that the foraminifers in
the massive sediments had thicker walls with more ornamentation, such as longitudinal ribs
and keels, than specimens of the same species from the laminated sediments. Although many
factors could influence the formation and preservation of laminae, they are often
interpreted to indicate an environment with low oxygen levels (<0.3 ml/l water;
Bernhard 1986).
If the changes are a response to the change in environment and do not
permanently alter the genetic make-up of the species, the generations after the
environment returns to normal will have their normal characteristics. Temporary changes in
the morphology of a species resulting from changes in its environment are called
ecophenotypic variation (Kennett 1976).

Foraminiferal Variability

Because of the many examples of variation in living and fossil
forms, foraminifers are considered to be extraordinarily plastic (Kennett 1976). A
foraminifer may contain enough genetic information to express many different forms,
depending on the conditions. The effect on gene expression (shape and function) of
environmental factors such as oxygen levels is a subject requiring further research.
Many of the so-called species in the fossil record were probably not
separate biological species. A species is defined as a potentially interbreeding group.
Fossil species can only be defined based on the characteristics of the preserved remains.
Species may be defined because of their stratigraphic utility. If a
group of fossil foraminifers contains a continuum of morphologic forms and one form is
found consistently lower in the geologic column than the other, separating them into two
or more species would increase the precision of the biostratigraphy based on their ranges.
It is quite possible, therefore, for a few types of created
foraminifers to have developed different forms to fill the various ecologic niches in the
pre-flood seas without the necessity of genetic changes requiring long periods of time.

PLAUSIBILITY OF A FLOOD MODEL

Number of Fossil Foraminifers

The first question which must be asked of the fossil record to
determine if it could have been formed in a flood scenario is quite simple. Are there too
many fossilized foraminifers for them all to have lived and died within the short time
allowed?
Answering this question quantitatively would require a detailed
analysis of the entire geologic column to estimate the number of foraminifers preserved.
Although foraminifers are found throughout the geologic column, they are actually quite
sparse in most sedimentary rocks. In Paleozoic and early Mesozoic strata, most specimens
are recovered from small fossiliferous areas. A micropaleontologist studying the Triassic,
for example, may process samples from a dozen localities before finding any specimens.
The number of foraminifers that could have lived between creation and
the flood is also difficult to estimate. The reproductive capability of foraminifers is
among the highest on Earth, with a doubling time of 3.65 days (Berger 1976). The pre-flood
conditions were likely good for rapid growth and reproduction. During and after the flood
the turbid waters would have included high levels of organic matter and other nutrients
needed to fuel growth.

Number of Species

The oceans today contain species which are zoned by depth and other
factors. If the pre-flood world contained several seas at different levels, as was
proposed by Clark (1946), separate morphological species could have developed to fill the
niches in those seas (Figure 1). Intensive differentiation could also have occurred during
and after the flood events as conditions changed. With the inherent plasticity in
foraminifer species discussed above, the many morphological species found in the fossil
record could have developed in thousands rather than millions of years.

FIGURE 1. A representation of pre-flood environments as proposed by Clark (1946).
The gradual erosion/burial of these ecologic zones by flood waters is used to explain the
fossil sequence in sedimentary deposits. Representation not to scale.

Distribution in the Fossil Record

The stratigraphic distributions of foraminiferal taxa are fairly
well described in the literature, but determining if that distribution could be the result
of a catastrophic flood is another subject which would require years of research.
A significant problem arises because similar forms are classified
differently if they occur at different stratigraphic levels. These cases are explained as
iterative evolution, that is, the same form evolved repeatedly through geologic history.
Thus classification is subjectively influenced by evolutionary theory. Repeated
occurrences could be explained as easily by a catastrophic flood model. If the
foraminifers found fossilized at various levels in the geologic column were living at the
same time in different ecologic zones, species common to several ecologic zones would be
found at several levels. Gaps in the record only indicate that the species was not present
in the source area or the ecologic zone being buried at that time, not that it was totally
extinct. No coincidence of repeated extinction and identical evolution is required.
Ecologic zonation as developed by Clark (1946) would mean that
foraminifers living in the lower seas or deeper parts of the ocean would be buried first
as the sediments were redeposited by the gradually rising flood waters, while those from
higher ecologic zones would be buried later The fossil record seems generally consistent
with this model. Figures 2 and 3 show the distribution of foraminifers today and of
fossils in the geologic column. Simple agglutinated forms that now live in environments
ranging from the deep sea to estuaries, are found fossilized in Early Paleozoic and
younger strata. Calcareous benthic species now predominate both in bathyal environments
(Figure 2) and in Mesozoic strata of the past, and presently floating planktonic forms
from a higher ecologic zone are abundant in the higher Cenozoic strata of the past.

In the oceans today, calcareous material is dissolved below the
carbonate compensation depth (CCD)  usually at a depth of about 4000 m,
depending on carbon dioxide concentration. Neither benthic nor planktonic calcareous
foraminifers are generally found below that depth on the abyssal plains or in deep sea
trenches, because their calcareous shells would be dissolved. Agglutinated forms are
dominant (Figure 2).
Agglutinated species are common in the Lower Paleozoic, and the benthic
calcareous foraminifers found generally have thicker walls than forms higher in the
geologic column. They could have lived near the pre-flood CCD where most calcareous forms,
especially thinner-shelled planktonic species, would have been completely dissolved. Lower
Paleozoic foraminifers are consistent, therefore, with the distribution expected by a
catastrophic flood.
The fusulinids in the Upper Paleozoic, however, are an anomaly. Some
species of fusulinids grew to volumes of more than 100 m3 (Ross 1979).
Foraminifers which grew that large today have symbiotic photosynthetic algae living in
their tests, and so must live within tens of meters of the ocean surface where sunlight is
available. Large foraminifers from other groups live in shallow water tropical
environments today; therefore, the fusulinids are interpreted also to have lived in a
similar environment (Ross 1979), yet we do not find them at the top of the geologic
column. Possibly they grew at the surface of pre-flood bodies of water of low altitude
(Figure 1).
Planktonic foraminifers are not found in Paleozoic or Lower Mesozoic
deposits. Even though living planktonic foraminifers float and would not be expected to be
found in the early flood deposits, tests of those which had died before the flood should
have been on the sea floor and should have been buried with those living there. Either
they were not present in those ecologic zones, or they were not preserved as fossils.
Because they have thinner, more porous tests than benthic forms, they could easily have
been dissolved preferentially on the sea floor before the onset of catastrophic flooding,
if their shells sank below the CCD.
Benthic hyaline calcareous foraminifers become abundant in the
Mesozoic. Triassic and Jurassic foraminifers are generally not as well preserved as later
forms. In Cretaceous strata, both benthic and planktonic forms are diverse and abundant,
making it correlative with the upper bathyal zone of the ocean today.
Foraminifers older than the Cretaceous are generally widely
distributed. A Triassic species may be found in both Australia and Idaho, but nowhere in
between (Tosk and Andersson 1988). Cretaceous and younger foraminifers have distribution
patterns correlative with modern assemblages (Sliter 1972). Under the prevailing paradigm,
this would mean that the pre-Cretaceous seas were more cosmopolitan because modern
hydrographic patterns and ecologic distributions had not yet developed. Continental
fragmentation and sea-floor spreading during the Cretaceous are used to account for the
development of modern oceanic patterns at that time.
In a flood model, however, this pattern is what would be expected.
During the more violent stages of the flood events, foraminifers from a small area would
be scattered widely over the earth. As the violence of the flood died down, foraminifers
would not be transported as far and might even begin developing their own ecologic
distribution patterns. Major deposition during and after the Cretaceous could have become
localized in basins and at continental margins. Life for foraminifers may have returned to
normal in less affected areas.

Post-Flood Foraminifers

Some foraminifers must have lived through the flood. Those that
could survive such a catastrophe would be forms tolerant of turbidity and strong wave
action, and possibly the juveniles of more delicate forms.
All major groups of foraminifers in the fossil record are represented
by living forms except the complex fusulinid group which dominated the Paleozoic. As
discussed above, they are interpreted to have lived in a tropical-type environment with
low sediment output, and they may have had little tolerance for storm conditions. The
agglutinated forms found in Paleozoic strata are found in many extreme environments today.
They may have been better able to withstand the flood events.
No particular biogeographic distribution would be expected of
foraminifers, unlike the animals which were saved in the ark and would have dispersed
afterwards. Foraminifers would have continued living wherever they happened to be after
the flood events subsided. With the availability of the many open niches and much organic
material stirred up by the flood, foraminifers could have multiplied rapidly. Roth (1985)
discussed the volume of biogenic sediments, especially foraminiferal oozes, on the ocean
floor and showed that it is plausible that the foraminiferal deposits found on today's
ocean floors could have been formed in the time since the flood.

CONCLUSIONS

The abundance, diversity and distribution of foraminifers in the
fossil record exemplify many of the problems of fitting the fossil record into a short
chronology, such as the multitude of species, large numbers of organisms, and apparent
evolutionary sequences of simple to complex forms. Living species of foraminifers exhibit
diverse morphological forms under varying environmental conditions, raising the
possibility that many of the nominal species in the fossil record are actually
ecophenotypes. In this case, a long time for evolution to take place would not be
required. Presumed evolutionary sequences could then represent populations living in
different environments or in the changing conditions during the flood and as it subsided.
Foraminifers are sparsely represented in the fossil record up through
the Triassic, with most specimens found in small fossiliferous deposits. [?? 12
October 2001] With this in
mind, and the fact that foraminifers can multiply rapidly, it seems plausible that the
number of organisms found in the geologic column could have been produced in the time
since creation.
The distribution of foraminifers in the fossil record seems to bear
some resemblance to their ecological distribution in the oceans today. Fossil benthic
species are found in most Phanerozoic strata, and similar forms are found living in
ecological zones ranging from the deep sea to brackish estuaries. Fossil planktonic
species are found only in Jurassic and younger strata, while living planktonic species are
found floating in the upper parts of the water column. These distributions seem consistent
with an ecological zonation model. The extinct large fusulinids in the Upper Paleozoic are
anomalous, however. They are interpreted to have had symbiotic algae, so must have lived
in shallow environments, perhaps in the upper ecologic zones of a low elevation sea.

REFERENCES

Bandy, O. L. 1953. Ecology and paleoecology of some California
foraminifera. Part 1. The frequency distribution of Recent foraminifera off California.
Journal of Paleontology 27:161-182.